Je le ferais nu, comme si je viens de sortir de la douche.

Deuxième choix serait en mangeant un bol de soupe.

This is not a good look...

You would use the screen share feature to display and discuss your work. I've had two "skype" interviews, one was a text only chat and the other was over webcam. I did wear a tie for the webcam interview. 

It's perfectly acceptable to ask them these questions before your interview.  And, yes, dress nicely.

This is great to hear. Citizen is right, ask them. One really cool thing is you are interviewing with a firm that is smart enough to even use something like Skype. It saves you travel cost.  

... and saves the firm expense in interviewing for an unpaid position. 

I agree, do not show them stuff on the webcam. You might want to put some of your stuff online somewhere or use screen sharing on skype. but that you should try beforehand with a friend, just to get the feeling of it...